.. _type-conversion:
Type Conversion
===============
.. index:: ! int(), ! str(), ! float()
.. index::
pair: type; conversion
Sometimes it is necessary to convert values from one type to another. A common
example occurs when a program receives string input, like ``"23"``, but needs
to use the value as a number.
Python provides a few simple **type conversion** functions that allow us to
change between data types. The functions ``int()``, ``float()`` and ``str()``
will try to convert whatever is in the ``()`` (the *argument*) into the types
``int``, ``float`` and ``string``, respectively.
The ``int()`` function takes a floating point number or a string and turns it
into whole number. Instead of *rounding* a decimal value, ``int()`` *discards*
the decimal portion of the number.
.. index:: ! truncate
.. admonition:: Example
Let's see ``int()`` in action. Run the following code and note how ``int()``
changes the decimal values.
.. raw:: html
New vocabulary! **Truncate**: Remove the decimal part of a number WITHOUT rounding.
What happens if we try to convert a string to an integer, but the string is not
actually a whole number? Add the following code to the editor above, then run
the program again. You should see an error message.
.. sourcecode:: Python
print(int("80days"))
print(int("12.34"))
In order for ``int()`` to work, the string has to be a whole number like
``'-2'`` or ``"526"``. Any string with letters, spaces, or punctuation will
throw an error. Modify the new examples by deleting the ``days`` and ``.``,
then rerun the program. You should see the integers ``80`` and ``1234``.
The type converter ``float()`` turns an integer or an allowed string into a
``float``. The type converter ``str()`` turns its argument into a ``string``.
Remember that when we print a string, the quotes are removed. However, if we
use the ``type()`` function, we can see the data type.
.. admonition:: Example
Let's see ``float()`` and ``str()`` in action.
.. raw:: html
Check Your Understanding
------------------------
.. admonition:: Question
What value is printed when the following statement runs?
.. sourcecode:: Python
print( int(53.785) )
.. raw:: html
Nothing is printed. An error is generated.
53.785
54
53
.. Answer = d
.. admonition:: Question
Which of the following generates an error message when passed to
``float()``? Feel free to try running each of the options.
.. raw:: html